This invention relates to a two-dimensional phase element such as a phase type computer generated hologram (CGH), a two-dimensional binary structure or a phase modulation plate, for example, usable as an optical component of a semiconductor manufacturing reduction exposure apparatus or a component of an optical interconnection element, for example. In another aspect, the invention concerns a method of manufacturing a mold for such two-dimensional element.
A paper xe2x80x9cO plus Exe2x80x9d No.11, pp95-100 (1996) discloses a method of manufacturing a step-like shape on a substrate, through repetition of resist application, resist mask patterning and etching. If the number of masks is L, a multiple level phase type CGH having a phase level of 2L is obtainable. FIGS. 24A-24C are plan views of reticles to be used for photolithography, in the manufacture of a phase type CGH. More specifically, FIGS. 24A, 24B and 24C show patterns of reticles 1a, 1b and 1c, respectively. Zones depicted by hatching are light blocking regions. The reticle 1a is used to perform an etching to a depth 61 nm. The reticle 1b is used to perform an etching to a depth 122 nm. The reticle 1c is used to perform an etching to a depth 244 nm. These reticles 1a, 1b and 1c may be used in any order. However, a higher resist patterning precision is attainable if the etching is started in an order from a smaller etching-depth reticle, that is, the reticle 1a. 
First, a resist material is applied to a substrate, and the resist is then patterned by using the reticle 1a shown in FIG. 24A. The thus produced resist pattern is then used as a mask, and an etching process is carried out to a depth 61 nm. The result is an etching depth distribution such as shown in FIG. 25A. Numerals in the drawing denote the etching depth (nm). Thereafter, the resist pattern is separated, and a resist is again applied to the substrate. Then, the resist patterning is carried out by using the reticle 1b shown in FIG. 24B. The thus produced resist pattern is used as a mask, and an etching process is carried out to a depth 122 nm, whereby an etching depth distribution such as shown in FIG. 25B is produced. Subsequently, the resist pattern is separated, and a resist is applied again to the substrate. The resist is then patterned by using the reticle 1c shown in FIG. 24C. The thus produced resist pattern is used as a mask, and an etching process is carried out to a depth 244 nm, whereby an etching depth distribution such as shown in FIG. 25C is produced.
In the photolithographic procedure described above, alignment of reticles is necessary. For manufacture of a multiple level phase type CGH,c idealistically a shape such as shown in FIG. 26 should be formed. Practically, however, there occurs an alignment error which causes an unwanted error at the edge of the shape, as shown in the sectional view of FIG. 27.
FIG. 28 is a plan view of a segment in a case where, due to an alignment error, a second-time resist pattern of a size xe2x80x9caxe2x80x9d at each side is deviated in X direction by a length xe2x80x9cdxe2x80x9d. Zones 11 depict the boundaries of segments defined by a first-time resist pattern. Zone 12 depicted by a thick solid line denotes the second-time resist pattern. Thus, zones 13 depicted by hatching are invalid regions as a phase type CGH, and the area S1 of the invalid regions can be given by:
S1=2adxe2x80x83xe2x80x83(1)
FIG. 29 is a plan view of a segment in a case where, due to an alignment error, a second-time resist pattern is deviated in x and Y directions by a length xe2x80x9cdxe2x80x9d. Zones 11 defined by narrow lines depict the boundaries of segments defined by a first-time resist pattern. Zone 14 depicted by a thick line denotes the second-time resist pattern. Thus, zones 15 depicted with hatching are invalid regions as a phase type CGH. The area S2 thereof can be given by:
S2=4adxe2x88x922d2xe2x80x83xe2x80x83(2)
On the other hand, where a phase type CGH manufactured in accordance with the method described above is incorporated into an illumination system, since the phase type CGH has invalid regions, light may be projected to an undesired position or the quality of an image formed by the phase type CGH may be deteriorated. Therefore, a desired performance may not be accomplished.
Where such an illumination system is incorporated into a projection exposure apparatus, a desired performance may of course be unattainable. Also, where a semiconductor device is manufactured by use of such a projection exposure apparatus, the yield rate may be lowered and the device productivity may be slowed down. It may cause an increased device price.
It is accordingly an object of the present invention to provide a two-dimensional phase type element and a method of manufacturing the same, by which a desired performance can be accomplished stably.
In accordance with an aspect of the present invention, there is provided a two-dimensional phase type element having plural segments, wherein an alignment error between segments is limited to a local portion.
In accordance with another aspect of the present invention, there is provided a method of manufacturing a two-dimensional phase type element, comprising the steps of: forming, on a substrate, a first etching mask in a checkered pattern; and performing an etching process while using the mask as a reference.
In accordance with a further aspect of the present invention, there is provided a method of manufacturing a two-dimensional phase type element, comprising the steps of: forming, on a substrate, a first etching mask in a checkered pattern; forming segments of multiple levels at a portion not covered by the first mask; forming a second etching mask corresponding to an inversion of the first etching mask; removing the first etching mask; and forming segments of multiple levels at a portion not covered by the second etching mask.
In the methods described above, the first etching mask may be formed by a chromium film.
The first etching mask may consist of aluminum.
The first etching mask may consist of aluminum and the second etching mask may consist of chromium.
The first etching mask may consist of chromium and the second etching mask may consist of aluminum.
The substrate may contain quartz.
A reticle having an optical proximity effect correcting pattern may be used to form the etching mask of checkered pattern through photolithography.
The etching process may be carried out by use of the etching mask and an etching mask formed by a resist.
The method may further comprise molding an element while using, as a mold, a substrate on which plural segments of multiple levels are formed.
The method may be usable to produce one of a phase type computer generated hologram, a two-dimensional binary structure, and a phase modulation plate.
In accordance with a further aspect of the present invention, there is provided an illumination system including a two-dimensional phase type element manufactured in accordance with a method as recited above.
In accordance with a yet further aspect of the present invention, there is provided a projection exposure apparatus having an illumination system as recited above.
In accordance with a still further aspect of the present invention, there is provided a device manufacturing method, comprising the steps of: exposing a wafer to a device pattern, by use of a projection exposure apparatus as recited above; and developing the exposed wafer.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.